Disclaimer:  Yet to use every weapon attachment in the world or gun. Obvious examples LMGs and Snipers with some ARs.  

Gunsmith I have saved my attachments so don’t have to remember or setup every time I change guns.

Assault rifles

Normally run quickdraw/stock everything apart from XR-2/Shevia/M8A7 and KN44.

High cailber used when going for headshots, long barrel would only use it on XR-2/M8A7 or HVK-30. Not sure would be worth using due to lack of ranged maps.

Shevia with stock/Elo

Suppressor for KN44 with stock is not bad.

SMG’s

Extended mag for kuda,  Quickdraw/laser for the VMP, Quickdraw for the Weevil, Fast mags / Extended mags or suppressor, Quickdraw / Stock for the Pharo , Red dot / Quickdraw for the Razorback.

Shotguns 

Nothing on the KRM or Quickdraw / long barrel

Nothing on the Brecci or Fast mags / Extended mags

Nothing on the Haymaker or Fast mags / Extended mags

Nothing on the Argus or Quickdraw / Stock

Suppressor can work on the Brecci makes the weapon 2 hit kill with less range.

Perks

Normally use the following pretty much

Blind eye/cold blooded for anything that needs to be destroyed and engineer

Flak jacket

Dead silence/Awareness or Dead silence

Tracker/hard wired

Engineer for red wood

Scavenger

Must be noted been running with only two perks as of late for certain gamemodes.  Fast hands/gung ho is good for shotguns plus ghost.

Equipment

EMP

Smoke

Trophy system

Thermite

Frag

Pretty much every class has black cell or XM-53 on it.  Apart from shotguns which uses a pistol.